Carriages / Wagons for Locomotion No.1

[What About The Bee]

I continue to be intrigued by the timing chain.  Such a novel feature.  

Stephenson and Dodds, in their patent, called the part that engages the chain a "wheel furnished with cogs".  When the wheel turns round, the projecting cogs enter the links, "completely preventing the chain from slipping"

Detail
Wood, Practical Treatise, 1825 

Examining the drawing, literally centuries later, the first thing that springs to mind is a sprocket and bicycle chain.  The description of function matches perfectly.  Indeed, the sprocket in the Wood drawing could very well be a bicycle sprocket.

Why would Stephenson and Dodds not use a bicycle chain?  Well, it hadn't been invented yet.  The primitive velocipede¹ was patented in 1817, two years after the Stephenson Dodds 1815 patent.  The bush roller / bicycle chain wasn't invented until 1880, 66 years in the future.

There is a better way to engage a chain than the method that  Stephenson and Dodds used.  That would be a "chain gypsy"² typically found on a windlass or capstan for raising and lowering an anchor chain. 

This provides excellent purchase on the chain.

The "double studded chain wheel" (chain gypsy) was patented by George Daniel Davis³ , who specifically claimed the construction of the chain wheel "so constructed that every alternate link of the [chain]  may lay flat upon the edge or circumference" of the chain wheel.   Patented in 1858, 44 years in the future for Stephenson and Dodds. 

Stephenson and Dodds, lacking a time machine, could not use a bicycle chain or a chain gypsy.  Hence the 'wheel with cogs' and chain.

In examining the chain coupling, I think it important to understand the purpose.  It was to retain the quartering between the front and rear axles.  Most steam locomotives, like Rocket and successors, are quartered across the axle.  The quartering is precisely fixed at 90°, since both wheels are hard mounted to that axle.

Chain coupled axles need not be so precise. Yet on these chain coupled locomotives, as long as one piston was still somewhere in the power portion of the stroke when the other was at top/bottom dead center; the locomotive would still start.  Therefore a few degrees of quartering error would not matter.  Indeed, Staniers 3 cylinder engines for the LMS show that quartering need not be at 90°.

The drawings show no idlers to take up tension and the drawing by Stephenson himself show the  chain to be slack.   A very near contemporary book: History and Progress of the Steam Engine, Galloway,1834 states what must be an innovation post patent.   Chains wear and the affect of the wear is called "chain stretch"⁴.  The innovation described was interesting. "When the chain got worn by frequent use, or was stretched, so as to become too long, one of the [axles] could be moved to tighten [the chain] again, until a link could be taken out, when the [axle] was moved back again to its former station".  They shifted an axle to set chain tension! This has a small affect on the angle of quartering, again, it is not significant.

The number of times the removal of a link could be performed is obviously limited.  Eventually, the links would wear through.  When replacing a chain, yachties are advised to replace the chain gypsy as well.  In Stephenson's case, that would be the wheel with cogs.

Bee

¹a two wheeled bicycle without pedals or chains.  Indeed, there was an early foot powered velocipede railway car noted in 1829.  Sadly, no images of this car exist (to my knowledge).  The car is fairly well documented in the press.

https://community.hornbyhobbies.com/forums/topic/35033-an-unknown-lmr-carriage-emerges-from-the-press/#comment-372391

² the actual term.  In the US, "chain wildcat"

³  text of Davis patent
https://books.google.com/books?id=8lzbPMbBLYcC&pg=RA12-PA1

Patent Drawing 

https://books.google.com/books?id=8lzbPMbBLYcC&pg=RA13-PP4

⁴ As a chain wears, the chain apparently gets longer.

 In actuality the inside contact surfaces of the links wear away.  This wear makes the center distance between two links sepatate.  When accumulated over many links the length of chain measurably increases.  Chain stretch.
 

[What About The Bee]

I thought to closely examine the chain itself.

Wood, Practical Treatise, 1825 provides us with an unusual description.  "This endless chain, which is now solely used upon these kind of engines, consisted at first of one broad and two narrow links, alternatively, fastened together at the ends with bolts; the two narrow links were always outside of  the broad link; consequently, the distance they were separated laterally would be equal to the breadth of the broad link, which was generally two inches, and the length three inches"

Quite the sentence and difficult to understand.  I puzzled over this sentence.  

Nicholas Wood was in a prime position to understand the Killingworth engine.  He was appointed an assistant colliery viewer at Killingworth, in 1811.  His superior?  Ralph Dodd.  Dodd, of course, the other patentee with Stephenson in 1814.  Indeed, Wood became Killingworth Colliery Viewer in 1815.  In 1818, Wood and Stephenson performed experiments with a dynamometer they designed, at Killingworth. ( https://community.hornbyhobbies.com/forums/topic/33593-railway-oddities/?do=findComment&comment=368416 ).  

Nicholas Wood was there and had genuine first hand knowledge. Wood was in a unique position to evaluate and describe the chain.  I do think this is the solution.

The blue links are 2" wide, 3" long.  Two yellow narrow links are on the outside of the blue link, as specified.  The red bolts go thru the blue and yellow links.  I've sketched in gray nuts, but these are not mentioned.  Take a moment to read the description from Wood as you study my solution to the chain.  The chain fits the description.

I was studying the (unfortunately low resolution) patent drawing for UK Patent 3887 Dodd and Stephenson.  I turned the drawing sideways, and wow, there it was.

UK Patent 3887
Dodd & Stephenson 

There is a long thin object drawn there.  Examining it in detail, I can see the side plates (yellow) and the blue links.  The ratios of width and length are not as described in Wood but there nonetheless, along with the red bolts.  That is typical of many patent drawings.  Deliberate proportional errors to throw off your competition.

So the real question now is the shape of the blue links.  Are they made of rod, like standard chain or are they cylinders, as I have drawn.

The rear elevation view of the "Killingworth Locomotive" (per Wood) shows the wheel with cogs and the chain.  The asymmetric object to the right on the axle is the eccentric for driving the slide valve.  Wood's Slip Eccentric, if you please. Returning to the wheel with cogs, we can observe the yellow side plates.  The blue links between the side plates show straight lines side to side, not curved.   So from this I conclude that the blue links are indeed cylinders

It is quite tricky in this end view to make out what is the wheel with cogs, and what are the blue links.  The yellow narrow links are clearly present however.

As the blue links are two inches wide, then the wheel with cogs must be just under two inches wide.  That is very robust sprocket indeed.  This chain can not twist and fall off the sprocket.  Once again, the resemblance to a bicycle chain is startling. 

The chain is such a unique railway feature, that it forms part of the patent claims and drawing.  

Bee

[threelink]

@What About The Bee  Hi Bee. Given that the blue links are, in effect, tubular and the red bolts appear not connected to the blue links in any way I wonder to what extent wear would have been a significant problem notwithstanding adjustment of the axle (what a job!) to maintain tension. I would imagine that the red bolts and the blue links must have moved in relation to each other quite substantially as the chain worked, particularly when passing round the sprockets, creating friction not necessarily overcome by the lubricants of the day. Your investigations of this early railway technology continue to fascinate.

[What About The Bee]

Hi ThreeLink 

16 hours ago, threelink said:

... when passing round the sprockets ...

Thank you for a thought provoking statement.  

There is a difficulty in the chain geometry that I am attempting to resolve.  When the chain is straight, there is no difficulty. My CAD matches Wood's verbal description and drawing, perfectly.  Yet when the chain goes round the wheel with cogs, there is an unresolved issue in matching the drawing.  

I will need a few days to reason my way through.  Please do bear with me.  I will make every effort to resolve the geometry issue and with it, answer the friction question.  

Bee

 

Edited September 17 by What About The Bee
A word was missing

[threelink]

Hello again Bee. This is me "thinking aloud" so to speak but it occurs to me that as the sprocket rotates the load on the chain is concentrated momentarily only on the lower or upper teeth of the sprocket , depending on the direction of travel. That being the case the remainder of the chain round the sprocket may be under far less load than I had first envisaged and therefor less prone to wear. Indeed, depending on the degree of adjustment in the axle position the chain links may go slack as they rotate about the back of the sprocket. I am sorry that this is couched in less than technical terms but I am a bit of a duffer when it comes to certain aspects of engineering and tend to work on instinct rather than knowledge.

I look forward to reading the results of your cogitations on the chain geometry.

[threelink]

And slackness would allow the blue links to rotate randomly so preventing localised wear by the red bolt constantly bearing against the same section of the blue link.?

[What About The Bee]

The Chain Dilemma

How, exactly, is the chain constructed?

Choice 1: The bolt is free to float inside the blue link, as I have sketched.  The bolts are 180° apart when the links are straight because of the tension on the chain.

Choice 2: The bolts are captive in bores located on the inside wall of the blue link.  The bolts are  180° apart when the links are straight because of the two bores.  In fact, the bolts are always 180° apart.

So what happens when the chain goes round the wheel with cogs?  I superimposed light pink circles with a center dot for each blue link to help see the solution.

For choice 1, the bolts aren't captive.  If we draw an orange line from blue link center to blue link center, then the yellow links should be on those orange lines.  

For choice 2, the bolts are captive.  Therefore, the pivot point is at each bolt.  The blue and yellow link lines, corresponding to blue and yellow links, are drawn to the pivot points.

Choice 2 appears to be wrong.

Examine blue link 5, on the straight.  The pivot points are 180° apart and the blue line passes through the center of the link.  Yet examine link 3.  The red line attaches to one pivot point and proceeds directly through the center of the pink circle.  If the bolts were captive, the yellow link would intersect the end of the red line, nearest link 4.  It does NOT.  Thus, the bolts are no longer 180° apart for link 3.  Similarly for link 2.

It appears, therefore, that choice 1 is correct. But! The yellow links are not exactly on the orange lines.  Go back to see.

With the chain geometry resolved, what about friction, and specifically, wear?

Assume the chain and wheel with cogs are perfectly sized.  The center distance from blue link two to blue link three fits exactly in the space in the cogged wheel for those links.  Precisely as drawn by Wood's illustrator.  The blue links nestle into the cogged wheel and the yellow link, being a precise fit, is drawn to the orange line.  Again precisely as drawn by Wood's illustrator.

The bolt, therefore, slides along the inside surface of the blue link, under the tension force.  I do not think the bolt rolls along the inside surface but I can be persuaded otherwise.  There will definitely be retarding friction and resultant wear, due to the sliding.

Sliding members are notoriously hard to lubricate.  The bolt will act as a wiper, pushing any grease or oil to either end of travel.  Thus, within a short time, the bolt will slide along the blue link, unlubricated.  The inside of the blue link will wear, as will the side of the bolt held against it.

As those surfaces wear, the chain stretches.  The center distance between blue links lengthens.  The yellow link will not be perfectly on the orange line, as it can and will droop away.  Similarly, the blue link will droop.  The wear on the inside of the chain will be reduced as members are not held under load.   This exactly matches your instinct, ThreeLink.

The outside of the chain will then wear, as will the cogged wheel, as the arc length in the cogged wheel and the chain center distance no longer match.  

Maintenance would be constant.  Replacing links is straightforward.  Wood mentions re-tensioning the chain which does not appear overwhelming.

Fitting a new cogged wheel, because it too wears, will be the most labor intensive.  Unless that cogged wheel is two halves that clamp around the axle, there aren't many other easy choices.   Replace the entire axle, wheels and all? Slide the cogged wheel off one side?    

Bee
 

Edited September 17 by What About The Bee
Apologies for the somewhat blurry images. I am working with what I have. These are small details, highly magnified. If I had better images, I would use them.

[LTSR_NSE]

@What About The Bee since neither of your choices perfectly fit the image (admittedly image could be to blame) is there a 3rd choice..?

Bolts are captive 180° from each other, however the (outside) narrow links aren’t perfectly straight, but actually describe a radius/arc, allowing the (inside) broad links to perfectly fit the cogged wheel.

[What About The Bee]

It cannot be that way @LTSR_NSE.  Captive bolts cannot move relative to each other on the circumference of the blue link, the point of the illustration with numbers.  How can the pivot point move, if the bolt is captive.  It cannot.  QED, the bolts are not captive.

Other simple explanations are

The illustrator was depicting what he saw, and that included wear.

The illustrator wasn't concerned about mechanical accuracy when it comes to a minor point.  The chains are fascinating to me (us?) but may not have held the same interest for the illustrator.  The sketch is reasonably accurate but imperfect.

Bee's pink circles aren't inserted to the nearest angstrom and this leads to angular errors.  

Any combination of the above.

When @threelinkasked about friction and wear, the exact detail of construction  became a critical input.  If the chain was constructed with captive bolts, the wear would be substantially different from free floating bolts.  That needed to be resolved first.  

I am more than happy to try other explanations.  That alternate must fit all the facts we know or can derive.  Sketch some blue and yellow links.  Ignore my interpretation, but do examine the Wood's illustration, the patent drawing and the verbal description.   Explain how the bolts move on the circumference from chain straight to chain on cogged wheel.

I think you will find the simple explanation on offer to represent a logical choice 

Bee

 

[threelink]

Hello again Bee. Taking a break from restoring some signage purloined over 50 years ago from the the abandoned and derelict Great Central Railway I took the opportunity to re-read this thread. I realised that I had failed fully to appreciate the function of the chain. I fell into the trap of thinking that its function was to transmit power so that it would be under constant load. If I have correctly understood the position its function was purely to maintain timing or quartering, the loco being an 0-2-2-0 rather than an 0-4-0. If I have finally got it right I am guessing that for so long as the wheels did not slip the chain would not be under any great tension, merely idling about the sprocket wheels - hence the slack shown in the various drawings. In those circumstances wear would be less. Clearly, if a wheelset did slip load would be imposed suddenly if not violently until timing was a re-established but presumably that state of affairs would persist only for a relatively short period. Perhaps wear was less of an issue than I imagined. I did say that I am a bit of a duffer, having had no engineering training... 

Thank you for yet more fascinating insight into early railway history. 

[What About The Bee]

Hi @threelink

The chain was replaced with coupling rods, when the second "Traveling Engine" made its way from Robert Stephenson & Co engine works.  Likely by very late 1825, or by 1826.  The S&DR complained that the second engine did not perform as well, in writing.

This is what leads me to believe the chain was present on Opening Day.  Active hauled an impressive consist, without complaint.  Hundreds of people and tens of loaded chaldrons, not to mention the Experiment passenger carriage.  That tremendous consist.  It beggars belief to suggest that was done with an experimental engine.  It had to be a Traveling Engine with understood mechanics.  The Hetton Colliery engines, the predecessors, all had chains.

I consider the Killingworth engine to be an 0-4-0, with the chains taking the place of the coupling rods.  The chains were to take care of quartering.

Bee

[threelink]

 HI Bee. Just to clarify my understanding of rods/chains and Whyte notations, I always considered coupling rods to be a means of transmitting power from a powered wheelset to an unpowered set. Hence a loco with 2 wheelsets, only one set powered but coupled by rods to transmit power to the unpowered set, would be an 0-4-0. A loco with 2 independently powered wheelsets (as I believe was the Killingworth loco and its cousins)  with a chain intended purely to maintain quartering and not to transmit power, would be an 0-2-2-0. 

I am sure you are right about Active being chain fitted on Opening Day. 

[What About The Bee]

I accept that I am likely wrong about the Whyte notation for these early Stephenson Traveling Engines.  The problem is that they do not neatly fit into that notation.  The two pistons really aren't independent, nor are they completely dependent.

This makes a muddle of fitting it into the notation.

Example 1:  the forward axle slips.  The chain, being connected to the rear axle which is not slipping, halts the forward wheel slip and all the power of both pistons is applied to the rear axle.

Example 2: The Traveling Engine is stopped. The rear axle is at top dead center.  Thus, the rear piston cannot apply power to the rear axle.  The forward axle, being ~90° out of phase, is at full power stroke.  Apply steam.  Does the chain merely keep timing, or is it applying torque to the rear axle?

Example 3: The chain breaks during operation.  Can the Traveling Engine make it back to the engine house?  I say yes.

Bee

 

[LTSR_NSE]

Example 1 & 2 would definitely correspond to an 0-4-0.

However (imo) Example 3 is more complicated… a more modern 0-4-0 (quartered wheels not axles) with broken coupling rod(s) would become a 2-2-0 & struggle more than the (chain-less) 0-2-2-0 except if wheel slip caused both of the latter’s pistons to be at 180° (or even worse at 0°) to each other!

Edited September 18 by LTSR_NSE

[What About The Bee]

A further confusion is evident in the patent drawing. 

Look at the side elevation.  The Traveling Engine is hauling a chaldron.  There is a strange little pony cart between the TE and the chaldron.  There is a chain!  It runs from the TE to the pony cart.

In the patent, Dodd and Stephenson provide the answer to what this is.  They explain that the TE is expected to haul ~60 tons, but if more is desired, the pony cart  is actually the tender and it can be made to increase the tractive effort.  

Applying the friction of the bearing wheels in this way, the engines propel 60 tons or upwards upon an iron railway.  If a greater burden is to be moved, the friction of other two wheels is added, and they are made to carry the water that supplies the engine.  A groove is made in each, and a groove in the last two bearing wheels of the carriage, into which an endless chain falls.  By the propelling force of the engine this is moved along, together with the bearing wheels of the water carriage attached to it.

The only other drawings of this pony cart are clearly derivative of the patent drawing.  

Caution is always advised with non-period drawings, but I find this one to illustrate the powered tender adequate.

Bee

 

 

Edited September 18 by What About The Bee
I hope this addendum provides insight into the chain. Dodd & Stephenson intended it to increase the tractive effort. The only way this can be so is if it transmitted power and not just timing.

[What About The Bee]

The Rev. John Brewster, "The Parochial History and Antiquities of Stockton-Upon-Tees...", first edition, 1799.  He updated and revised the tome, a second edition, which was published in 1829.  An exciting lead, indeed, because of the railway! When I first reviewed the second edition, I was incredibly disappointed.   

Whilst he does use the word "railway", there are only 16 occurrences.  In hundreds of pages, only 16 occurrences of the word.   Further, those 16 are clustered in a yet another re-telling of Opening Day.  One I had seen repeated many, many times.  The typical recounting of passengers and freight.  The recounting is only interesting if not previously encountered, anywhere else.  Apparently, the Rev Brewster did not care much for railways.  So I bid the Rev Brewster a good day and moved on.  How wrong I was.

Tucked away, in an appendix, is this marvelous sketch.

The text refers us back to the text about Opening Day, so we can be sure that this locomotive operated on the S&DR.  Yet, it cannot be Active.  It cannot be the locomotive used on Opening Day.  

Why not?  Because it depicts the parallel motion which only came on later locomotives.  The double criss-cross of that motion betwixt cylinders is fairly distinctive.  The slide bars depicted for the Killingworth Engine and Active are quite a bit different.   If you go back through this thread, you can see many depictions if the slide bars, but almost no depictions of the parallel motion.  Here is one and it is from 1829.

George Stephenson's exarsting pipe (blast pipe) is present, connecting the exhaust from both cylinders to the chimney.  This feature can be observed on the Hetton Colliery locomotives, so it is no surprise here.  

Further, we have a depiction of the coupling rod, the successor to the chain.  Proof that coupling rods were used on S&DR locomotives, but given the 1829 date, not proof of use on Active.

The drag chain is shown behind the chimney, implying chimney to the rear as it dragged chaldrons.  Interesting.  See my yellow arrow in Brewster's sketch.

That vertical rod centered between the sweep (connecting) rods is apparently to control the valve timing.  There should be two rods, of course, one each for the slide valve timing of each piston / axle, both on the same side, as depicted in better drawings.

On the whole, the drawing is exciting for the 1829 date and what it portrays.  It is so inexpertly drawn that details may not be vacuumed from the sketch. The piston rod closest to the chimney is not centered.  The parallel motion is grossly incomplete.  Where is the footplate running down the side?

The public's attention was turning to that vast new Stephenson project, the Liverpool & Manchester Railway.  Grand tunnels and new locomotives.  Elegant new rolling stock.  The S&DR seems rather quaint by comparison, even if only 4 years old. 

A drawing of an S&DR locomotive, after 4 years of railway evolution, even when poorly drawn, is priceless.

Bee

https://babel.hathitrust.org/cgi/pt?id=hvd.32044081229080&seq=7

 

[What About The Bee]

'Common knowledge' says that Active was the first locomotive with coupling rods.  This is repeated everywhere you look, sometimes with the word "probably".  I present herein some reasonable contrarian arguments for your consideration.  

Can I unequivocally state Active had a chain on Opening Day?  No, I can not. 

Can I unequivocally state Active had coupling rods?  By May of 1827, yes I can, clearly so.  But what of Opening Day on the Stockton and Darlington Railway.   That's a horse of a different color.

PART 1, The Letter 

The second Traveling Engine presented to the Stockton and Darlington Railway was named "Hope".  

List of the first Traveling Engines on the S&DR, Wood, Practical Treatise, 1838

Delivered to the S&DR in October 1825.  This TE was the one that gave so much trouble to the S&DR, with its novel features not trialed before delivery.  The locomotive that caused the S&DR to admonish Robert Stephenson and Co about sending untested equipment.

We do have a letter from George Stephenson to Timothy Hackworth, the first Superintendent of the railway at the S&DR.  A position Hackworth held until 1840. That Timothy Hackworth, of San Pariel and Rainhill fame.

Dated 12 January 1826, a mere 3½ months after Opening Day.

÷÷÷

"Dear Timothy 

"If you have any fear or trouble with the cranks, let me know by return of post, and I will send the long ones over and two single crank pins to fit the large holes of the wheels.  It appears to me that one of the side rods must have bent to let the other  get over the centre, otherwise it could not get past.

"How does the new plan of wheels do?  Is there any appearance of working loose?  How does the old engine get on?

".... [some unimportant matters for this discussion follow]

"I am, Dear Timothy, Yours Sincerely

"[signed] Geo. Stephenson 

÷÷÷÷÷

The first thing of note is that George is discussing  two Traveling Engines.  Active (Locomotion) and Hope.  This is clear from the explicit reference to the "old engine".

George uses the word cranks and further on, crank pins.  There is only one identifiable crank (not crank pin) on these Traveling Engines, and that is the return crank on the wheel for quartering.  Note that there must have been a problem with these return cranks, as George constructs a sentence so as to assuage Hackworth's concerns.

George uses the phrase "side rod".  Newton's London Journal in 1825, calls the rods running down from the cross beam "sweep rods".  George clearly communicated with Newton, and I find it strange that George would communicate independently with both Newton and Hackworth in such a short period of time, and call rods by different names.  Thus "side rods" cannot be "sweep rods".  From earlier discussion, we know "sweep rods" are connecting rods, the rods that connect the piston to the wheels.  Are the "side rods" the elusive  coupling rods, that couple wheels together?   

George states that a side rod must have bent, to allow the other to get over center.  This cannot be a sweep rod, since the left and right sides of an axle have identical quartering.  There is no way to change the quartering phase on a singular axle, to get over centre, no matter how the sweep rod is bent.  Thus, a side rod must refer to what is now known as a coupling rod.  

On a TE, the coupling rods are always in perfect phase with each other.  Unlike a more modern steam locomotive, the coupling rods match on the left and right sides.  They are not 90° out of phase.  When the coupling rod is most forward, and begins its stoke to the rear, there is an uncertainty which way the other end of the rod will go, up or down.  On a more modern steam locomotive, that doesn't matter, since the coupling rod on the other side is quartered and thus keep the uncertainty from having any effect.  But when both rods are in phase, the uncertainty can cause the coupling rods to criss cross.

Put another way, the front axle has the coupling rod positioned as far forward as it can go.  Both sides are the same.  The front wheels turn a fraction more.  Both coupling rods are moved to the rear.  The uncertainty drives the left coupling rod up, the right coupling rod down.  This force could certainly bend rods and move return crank phasing.  Can't happen when the opposing rods are 90° out of phase, but these rods are perfectly in phase. 

Additionally, if a side rod is bent, as George theorizes, then it may never get over center and be forced back from whence it came.

George then asks how does the new plan of wheels do.  The spokes take up all the forces.  The spokes can obviously break.   And Timothy Hackworth does complain of the wheels in November 1825, requesting replacements.

Exactly what the new plan of wheels was is not recorded.  If you look at Brewster (previous post), you may detect a ring on the wheel where the sweep and side rods connected.  The plan there was all the spokes are connected by a ring, presumably of metal.  Another plan was the one we see reported by the Prussian Engineers who visited the S&DR in May 1827, the two part plug wheels we see on Locomotion today.  Essentially a ring of cast iron centered on a cast disk of iron with oak centering plugs.  

No need for a dramatically stiffer wheel or spoke, if the forces are transmitted through the chain. Only  coupling rods demand stiffer wheels.

And, then, by the way, George asks "How does the old engine get on?"

Note the location, at the very end of the discussion on the traveling engines.  Almost an afterthought, it distinguishes itself from what came before.  There is no need to denote the "old" engine, except to differentiate it from the new engine.  In my view, all that comes before that sentence is about Hope, the new engine.  Why ask about the old engine if it is identical to the new engine?  Indeed, if identically configured, the discussion would apply to both.  But George specifically asks about the old engine.  Telling.

Plenty of evidence here that Hope had coupling rods.  But evidence for Active?  

PART 2: The Load

The much repeated load on Opening Day was: five waggons loaded with coal, with passengers sat on the top; one waggon with sacks of flour, with passengers amongst them; one waggon with ‘surveyors and engineers’;
Experiment passenger carriage in which the railway’s directors and ‘other proprietors’ were seated;
six waggons filled with ‘strangers’;
fourteen waggons filled with workmen and others;
six waggons loaded with coal with passengers sat on top.  The passenger count was estimated to be 700 persons, with the total load estimated, at the time, to be 80 tons.

In 1832, it was empirically found that 8 pounds of force were required to move a one ton weight on rail.  Now we can expect that more force was required to move a ton in 1825, but the figure will serve as an interesting strawman.  Tractive effort of 8 pounds per ton.  On Opening Day, the load was estimated to be 80 tons.  Therefore, Active must have produced at a minimum 640 pounds of tractive effort.  We also know the velocity on Opening Day was a mind blowing 4 mph!  Crushed to atoms by the extreme velocity!  If I have done the maths correctly, that equates to 6.8 horsepower, or just a little less than a riding lawn mower.  

What I am concerned with is the force applied when the side or coupling rods criss cross. The pistons are 9" diameter, yielding an area of 63.62 in².  As Active operated at 30 psi, the linear thrust will be 1908.6 lbf. That is a significant amount of force, which could bend a long coupling rod, move a return crank or break a spoke.   

I ask myself, why was Active capable of handling these forces, when Hope was not.  

A chain transfers forces through tension, it cannot transfer forces via compression.  We cannot push a string, it simply does not work.  A coupling rod transfers forces in both tension and compression.  When the uncertainty in direction causes the coupling rods to criss cross, the compressive forces applied can cause the noted failures. 

Further, a chain applies forces to the wheel with cogs, a 2 inch wide sprocket.  A side rod applies forces to a spoke on a wheel.  Spokes are excellent in compression when the axle is over the felloe.  But a force applied laterally between the hub and felloe is a bending force.  The spoke could have been designed, had they modern beam bending theory.  They did not, material sciences in 1825 wre not as they are today.  Instead, they went for rings and plug wheels.

And yet, Active did not experience the failures.  But Hope did.  Telling.

Part Three

'Common knowledge' says that Active was the first locomotive with coupling rods.  This is repeated everywhere you look, sometimes with the word "probably".  Hope clearly did have side rods per George Stephenson in 1826.  Hope arrived shortly after Active.  But that simply does not mean nor require Active to have side rods.

As late as 1923, Young writes that Locomotion was originally fitted with parallel motion.  Clearly an error, the contemporary depictions are all slide-bar.  Young also asserts Locomotion had coupling rods on Opening Day.  The evidence he presents is that Hackworth proposed coupling rods before his departure from Robert Stephenson and Co in 1824.  Active was delivered in Sept 1825.  That is scant evidence indeed.  Hackworth was not present as Active was rushed to completion.

In 2023, Bailey and Davidson drop the parallel motion assertion for opening day and agree it was slide bar.  I agree. They still assert coupling rods, but cover their bet by including the word "probably".

What is certain is that the transition from chain to coupling rods did occur at the S&DR. Locomotion was likely converted to coupling rods at the same time it was converted to parallel motion.  By May 1827, with the report of the Prussian Engineers, we know that Locomotion had parallel motion.   Locomotion had the slide bar arrangement from Sept 1825 to May 1827, or 20 months at the most; likely far less.

In 1827, Hackworth constructed Royal George for the S&DR, an 0-6-0.  The pistons are moved to either side.  Axles are quartered by side not by axle.  Coupling rods present

"Royal George"  S&DR No.5 1827 Drawing from "The Engineer" 1857.

In 1829, Hackworth presented San Pariel, an 0-4-0, he utilized proper coupling rods, definitely properly quartered.  

Mechanics Magazine, 1829.  San Pariel

There is no doubt that Hackworth championed coupling rods.  He would have been quite influential in his role as Superintendent of the locomotives at the S&DR.  

Bee